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F. FISHER. TALKING STRAP FOR TELEPHONE SWITCH BOARDS. No. 314,819. Patented Mar. 31', 1885.

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' CLU UNITED STATES PATENT OFFICE.

FRANK E. FISHER, OF DETROIT, MICHIGAN, ASSIGNOR TO THE DETROIT ELECTRICAL 'WORKS, OF SAME PLACE.

TALKING-STRAP FOR TELEPHONE SWlTCH-BOARD S.

SPECIFICATION formingpart of Letters Patent N0. 314,819, dated March 31, 1885. Application filed October 18, 1884. (No model.)

T 0 all whom it may concern.-

Be it known that I, FRANK E. FISHER, of Detroit, in the county of Wayne and State of Michigan, have invented a new and useful Improvement in Talking-Straps for Telephone Switch-Boards, of which the following is a specification. I I

Figure 1 is a perspective of the strap. Fig. 2 is a perspective of the connecting-plug. Fig. 3 is an end view of the connecting-plug. Fig. 4: is a front elevation of a portion of a switchboard, showing one talking-strap; and Fig. 5 is an out-line view of part of three switchboards, showing the connection between them.

My invention is intended for use in telephone-exchanges arranged upon the group system, where it is necessary to make connection between two switch-boards in order to connect two subscribers whose lines terminate at different switch-boards; and it consists in a device whereby an operator at one switchboard in calling a switch-board at her right cuts off from the circuit of the strap all switchboards at her left, and vice versa, and in the act of breaking connection restores the circuit through the strap. so that it is impossible to leave a subscribers line open in the exchange.

A represents a portion of a switch-board.

13 represents a metal piece projecting through ahole in the switch-board, and cast on a metal shield, H, which is screwed to the switchboard. P represents a cylindrical piece of metal cast on or secured to shield H and projecting forward of the switch-board. Its end is somewhat pointed, and a groove, f, is cut around the base of the point. C C represent two metal springs, which are fastened to B by slipping the threaded shank M, which is part of B, through holes in right-angled ends of said springs and screwing the nut N on said shank. Springs C C are insulated from each other and from B by strips of insulating material, X. These springs C C pass through slots 0 in shieldH and press against cylinder P, so that they are thus in electrical communication.

F represents a wire or conductor, which connects spring C on the switch-board at one end of the exchange with the ground G, then connects C on said switch-board with spring C on the next switch-board, and so on through all of the switch-boards in the exchange, the last being grounded, as shown in Fig. 5. This forms a complete circuit or talk-strap through all the switch-boards, and as many of these straps or circuits are put in as are necessary to accommodate the business of a given exchange.

X represents insulating material (rubber, &O.) wherever used in the drawings.

D represents a plug for making connection with the talking-strap. It consists of a metal body, D, preferably rectangular, having a hole, K, drilled therein longitudinally and large enough to just easily slide over cylinder P.

Y represents the handle of the plug, made of any suitable non-conducting material, and a flexible connecting metalliccord passesthrough this handle and is connected to the metal part of the plug, the other end of said cord being connected with a plug adapted to make connection with a line-switch, as described in an application for a.patent heretofore made by y me and now pending.

E represents a piece of metal secured at one side of D, but entirely insulated therefrom. This strip of metal E is only a facing for the insulation X, to protect it and afi'ord asmooth sliding surface, and may be dispensed with by making the insulating material of somehard smooth material, such has hard rubber, glass,

L represents a spring secured to Dand having its free end bent into a V shape, as shown at Q, the point thereof lying normally in a slot cut through D into hole K. It is obvious that this construction of spring L renders it impossible to force plug D over cylinder P, except when the plug is in such a position that spring L will pass between springs C C with out coming in contact with either, and that when the plug is forced over cylinder P the V portion of the spring L will engage with notchfand hold the plug in position. The act of forcing the plug over cylinder P forces springs C C away from P, thus breaking the contact which afforded electrical communica tion between the springs.

The end of plug D may be slightly beveled,

and the extreme ends of O 0 turned outwardly to facilitate the entrance of the plug between the springs.

The operation of my invention is as follows: Suppose the switch-boards A each contain fifty lines, that the talking-strap shown is No. 1, and that subscriber 51 on board A wishes to talk to subscriber 150 on board A. Subscriber 51 calls the exchange, and, when in communication with the operator in charge of the board A, asks for No. 150. The operator forces plug D on cylinder in such mannerthat the insulated strip E comes in contact with spring 0, and thus cuts off board A and all I 5 boards on the same side, because electrical communication between spring G and cylinder P on board A is broken by means of the insulation between strip E and D, while the circuit between boards A A and all boards 2c on the same side is not affected. The opera- 0 together.

It is evident that the two grounds at the ends of the talking-strap are entirely out out, so that they do not interfere with the telephonic circuit. 7

When the signal for disconnection is given, the act of pulling off either plug D restores the ground at the end of the talking-strap, so that if either or both operators forget to disconnect the subscribers line from the strap such line is always grounded and the subscriber can operate his annunciator, thus obviating the present difficulty experienced from occasionally leaving a subscribers line open in the exchange.

What I claim as my invention, and desire to secure by Letters Patent, is-

1. A talking-strap for switch-boards in a telephone-exchange, consisting of a metal piece fixed in each switch-board, having a pointed metal projection, and having fastened thereto switchboard with the ground, and a plug adapted to slide over said pointed metal piece and break the contact of said springs there with, and having one of its surfaces insulated from the rest of the plug, substantially as shown and described.

2. A talking-strap for switch-boards in a telephone-exchange, permanently grounded at each end, wherein the circuit in each switchboard is composed of two insulated contactsprings normally in contact with a common electrical conductor, in combination with a connecting-plug adapted, when placed in position, to break the contact of said springs and their common conductor, and having one side thereof insulated, substantially as shown and described.

3. In a telephone-exchange, the combination of the switch-boards A A, &c., metal pieces 13, each having the projection P, with groove f, insulated contact-springs O O, and conductors F, substantially as shown and de scribed.

4. In combination withatalking-strap connecting the switch-boards in a telephone-exchange, and consisting in each board of the metal piece 13, projection P, and insulated contact-springs O O, the connecting-plug D, having the insulated side E, substantially as shown and described.

5. In a talking-strap for telephone switchboards, the combination of the metal piece B, projection P, having thereon the groove f, insulated contact-springs GO, and plug D, having spring L, with V-shaped part Q, adapted to engage with groove f,and insulated side E, substantially as and for the purposes set forth.

6. A talking-strap for switch-boards in a telephone-exchange, permanently grounded atjeach end, and consisting at each switch-board of two contact-springs insulated from each other, but in contact with a metal piece adapted to receive and holdaconnectingplug when said plug is not in use, substantially as shown and described.

7. A talking-strap for switch-boards in a ICO 

